Today there is a class of PCI Express boards that are dedicated for the multichannel wireless communication market. The main feature of these boards is that these boards use different wireless modules or blocks located on the PCB surface. Most of these wireless modules are implemented in a MiniPCI Express or M.2 form factor.
The wireless module itself or wireless modules in MiniPCI Express or M.2 form factor are significantly higher than standard electronic components that can be placed on the PCI Express board PCB.
The PCI Express add-in board specification limits the height of the components that can be placed on each side of the PCB. The maximum height of components on the primary component side (top side) of a PCI Express add-in card can't exceed 14.47 mm, and the maximum height of components on the bottom side (also referred to as the soldering side) of the PCI Express add-in card can't exceed 2.67 mm (according to the PCI Express Specification). These requirements essentially limit the possibility of using the bottom side of the PCI Express board for high electronic components or wireless modules placement.
The development road map of modern personal computers (motherboards) is moving towards reducing the quantity of PCI Express sockets for connecting add-in PCI Express boards. The most popular motherboards have one or two ×16 PCI Express connectors. As the result the number of add-in PCI Express boards that can be connected to the motherboard decreases.
Therefore, efficiency of PCI Express board surface utilization and increasing the number of electronic components or electronic modules on the PCI Express board are becoming top priorities.
The well-known way to increase the number of electronic components or electronic modules on the PCI Express add-in board is using so-called daughter boards that mechanically and electrically are connected to the PCI Express add-in board. These daughter boards are located in parallel to the add-in PCI Express boards and mount on the top side of them.
U.S. Pat. Application 20140365714 (P. Sweere, et al) represented an additional daughter-card (PCB), on which additional electronic components are located. Said daughter PCB is located in parallel to the add-in PCI Express board. The total height of the components that are located on the top surface of the PCI Express add-in board together with daughter board components and the thickness of a printed board of said daughter board can't exceed the value of 14.47 mm that is defined by PCI Express Specification. The daughter board is connected to main add-in PCI Express board via “a flash daughter-card connector”.
U.S. Pat. No. 8,639,863 (P. Kanapathippillai, et al.) proposed to use multiple daughter boards located on the top side of the PCI Express add-in board in two layers. The total height of the components from the top side surface of the PCI Express add-in board including the daughter board components and daughter board PCB thickness can't exceed the value of 14.47 mm. Therefore, the height of components located between the top side surface of the PCI Express add-in board and the bottom side surface of the daughter board and height of the components on the top side surface of the daughter board are significantly limited.
Solutions with daughter boards have four main disadvantages. First, air flow between daughter boards and PCI Express add-in board is limited, and the placement of electrical components that can generate significant amounts of heat between the daughter board and PCI Express add-in board (top side) is not possible.
Second, the traditional PCI Express add-in board with a daughter board on the top side can't utilize the 2.67 mm space on the bottom side of the PCI Express add-in board for high electronic components or modules placement (like transformers, relays, capacitors etc.).
Third disadvantage is that by using any additional daughter boards the maximum height of electronic components that can be located on the top side of the PCI Express board is reduced by the value equal to the daughter board thickness. And the resulting maximum height is divided by daughter board. That makes it practically impossible to install electronic components with a height of more than 4 mm.
Fourth disadvantage is that all known standard solutions with daughter boards cannot be used for the placement of multiple replaceable modules (for example wireless modules in MiniPCI Express or M.2 form factor that can have height more than 6 mm). Even if the modules are placed between the daughter board and PCI Express add-in board, they are then not accessible for replacement.